Power amplifiers are used in radio base station products for cellular telephone networks such as CDMA and OFDM. They may also be used in other wireless networks, such as WiMax and others, and provide amplification of microwave and radio frequency signals for transmission. Several different configurations of operation of power amplifiers have been used. A first traditional configuration is referred to as a conventional 2-way combined class AB mode. In this configuration, a pair of amplifiers are both operating to amplify one half of the signal to be transmitted. A higher efficiency configuration is referred to as a 2-way Doherty configuration. In this configuration, two transistor stages are combined. One stage is a main amplifier, and the other is an auxiliary amplifier. At low power levels, the auxiliary amplifier is operating in a cutoff mode, and does not significantly contribute to the output. At higher power levels, the auxiliary amplifier contributes to the output, and moves toward equal contribution at the highest power levels.
The conventional configuration provides lower efficiency, but also lower electrical memory effects. This requires a less sophisticated predistortion linearization algorithm to meet conducted spurious emissions requirements. The higher efficiency Doherty configuration exhibits much higher electrical memory effects, and thus requires a much more sophisticated predistortion linearization algorithm with memory correction.